1. Field of the Invention
The present invention relates to an apparatus for introducing a reducing agent, which in particular contains urea, into the exhaust of an internal combustion engine, having a reservoir, a delivery unit, and a flow path for the reducing agent, and having a ventilation device for ventilating at least one region of the flow path.
2. Description of the Prior Art
An apparatus for aftertreating the exhaust of an internal combustion engine, known from DE 101 16 214 A1, stores a urea/water solution in a reservoir and delivers it to a mixing chamber by a delivery pump. Compressed air is blown into the mixing chamber. The resulting aerosol of compressed air and urea/water solution is blown into an exhaust line upstream of a catalytic converter. In this case, the urea serves to reduce NOx in the catalytic converter.
The previously known systems operate with a diaphragm pump to supply the urea/water solution but their delivery capacity is reduced when air is present in the flow path on the suction side and in particular in a pump head, and the system must therefore be bled. In the known apparatus, bleeding occurs by means of a solenoid valve that must be triggered by a control unit. In the operation of this solenoid valve, however, it has turned out that even when the solenoid valve is open, it is not always possible to assure the ventilation of the flow path for the reducing agent.
The object of the present invention, therefore, is to modify an apparatus of the type described above so that it functions in the most reliable way possible.
This object is attained in that the ventilation device is situated at a geodetic high point of the flow path and in that the ventilation device has an opening, which permits a constant return of a minimal fluid quantity to the reservoir.